Testing for Physical Purity - Seed Testing - page 42

A noxious weed seed examination is usually performed in conjunction with the AOSA purity test.
Perhaps the best deinition of a noxious weed is a plant that is declared by law or regulation as noxious. The
federal noxious weed seed list in the United States speciies weed species that are prohibited when seed is
sold in interstate commerce. Moreover, each state law or regulation has established its own list of noxious
weeds that are noxious within the state. State noxious weed lists include primary or secondary weeds.
Primary or prohibited noxious weed seeds are those that are prohibited in seed lots sold or offered for sale.
Secondary or restricted noxious weed seeds are those that are allowed in restricted levels in seed sold or
offered for sale.
EQuIPMEnT And THE WorkInG EnVIronMEnT
Laboratory Space and Light
The purity testing section of a seed laboratory should be designed with special attention to lighting. The
use of natural daylight should be provided whenever possible from large windows facing to the north and
extending downward to desk level. This arrangement allows minimum dependence on use of supplemental
lighting and provides the best conditions for making precise determinations where small differences in
color, texture, and shape are critical. It is also believed that natural light causes less eyestrain and fatigue
than that from artiicial sources. When supplemental light is required, it should be provided from individual,
adjustable, multiple-tube luorescent lights of the cool-white type which most nearly duplicates natural
daylight.
desks and Workboards
Purity separations have traditionally been performed on diaphanoscopes, wooden workboards equipped
with a drawer or pan in front and arm rests on either side. Such workboards should rest on desks or tables
of convenient height to provide maximum comfort to the analyst throughout several hours of exacting and
intense, painstaking work. Some laboratories have tables and/or chairs that allow analysts to adjust them to
any desired height.
Figure 4.2. Two kinds of conventional purity stations found in seed laboratories. Forceps, hand lens, desk
lamps, or lighting magniiers are basic requirements for the traditional purity work station.